1. Field of the Invention
The invention relates to a process for preparing quaternary ammonium substituted carbonate esters useful as bleach precursors in detergent compositions.
2. The Related Art
Peroxygen compounds such as sodium perborate are ineffective at bleaching fabrics under wash-water temperatures below 60.degree. C. Good low temperature performance can however be achieved through combination of the peroxygen compound with a precursor as activating agent.
A recently issued patent, U.S. Pat. No. 4,751,015 (Humphreys et al), reported an unusually effective family of bleach precursors identified as quaternary ammonium substituted peroxy carbonic acid esters. Various synthetic routes have been proposed to obtain these materials.
One route involves the reaction of an alcohol such as cholyl chloride with phosgene in an aprotic organic solvent to form a hydrogen chloride complex of a cholyl chloroformate. Subsequent thereto, the chloroformate is combined with a second hydroxylic material such as phenol sulfonate. See U.S. Pat. No. 4,988,817.
Another synthetic avenue is described in U.S. Pat. No. 4,985,561. Therein is reported the reaction of an aryl chloroformate with sulfur trioxide forming an aryl sulfonated chloroformate. This intermediate is then condensed with a quaternary ammonium substituted alcohol such as cholyl chloride.
There are several problems with the aforementioned synthetic schemes. Both require phosgene chemistry and the concomitant elimination of hydrogen chloride during the esterification steps. Hydrogen chloride is highly corrosive to equipment. Capital expense is therefore significantly increased. Pollution problems also arise with the generation of acid by-products. The phosgene route also forms considerable quantities of sodium chloride which are not easily removable from the desired products. Sodium chloride is hygroscopic and adversely impacts upon stability of the desired carbonate esters.
Transesterification has been proposed as a route to obtain carbonate esters. U.S. Patent 2,691,017 (Dornfeld) reports syntheses of bis-aminoalkyl carbonate derivatives through transesterification of diethylcarbonate with alkylamino compounds followed by quaternization of the amine group. From this reference there is no indication that an asymmetric displacement with aminoalkanol onto the reactant carbonate would be achievable. There is also no teaching as to how a sulfophenol ester could be formed through this transesterification route.
A still further method of achieving quaternary ammonium substituted carbonate esters is reported in a concurrently filed U.S. application Ser. No. 582,278. Therein is disclosed transesterification of low molecular weight carbonates, e.g. diphenyl carbonate, with quaternary ammonium functionalized alcohols, e.g. choline chloride. The problem with that route is that only a small percentage of the asymmetric carbonate is formed; the major product is the symmetrical bis-substituted quaternary ammonium functionalized carbonate ester.
Accordingly, it is an object of the present invention to provide an improved synthesis of quaternary ammonium type carbonate esters.
A more specific object of the present invention is to provide a route to quaternary ammonium type carbonate esters not involving generation of any hydrogen chloride by-products.
A still further object of the present invention is to provide a synthetic route to quaternary ammonium type carbonate esters through an environmentally friendly procedure and wherein good yields are achievable of asymmetrically substituted carbonate esters.
These and other objects of the present invention will become more readily apparent upon consideration of the detailed description and examples which follow.